Interoperable train control (ITC)—positive train control (PTC) systems include on-board units (OBUs). The OBU provides a safety overlay for railroad operations through brake enforcement. However, in some cases a malfunctioning OBU cannot or does not release the brakes and thus disallows train movement. In order to overcome such situations, a hardware cutout switch can be used to physically isolate a malfunctioning OBU from a locomotive's brake system.
Situations may occur where the erroneous enforcement is not the result of a malfunctioning OBU, but is the consequence of another faulty element within the ITC-PTC system (e.g., a wayside interface unit (WIU) that is unable to communicate). Utilizing the hardware cutout in such cases may be ill-advised, since the fault does not originate within the OBU and therefore prohibiting OBU operation may decrease operational safety. On the other hand, resolving the situation may require a considerable amount of time and thus a substantial loss of revenue for the railroads.
A software cutout can address the erroneous enforcement issue. However, a software cutout is not tied to any operational condition and thus is not limited in its effect. An example of a conventional software cutout use case is as follows:                OBU is in a state providing PTC functionality where the crew determines a need to cutout the OBU without using the hardware cutout switches.        Crew selects the cutout softkey.        OBU prompts for confirmation.        Crew confirms prompt.        OBU transitions to the cut-out mode (with appropriate display changes and back office server (BOS) report messages) and disables PTC enforcement.        Crew can then proceed to operate the train on PTC track without PTC enforcement.        When crew determines PTC should be re-engaged the crew selects the cut in softkey.        The OBU performs an abbreviated initialization to ensure data is up-to-date and transitions back to active (with appropriate display changes and BOS report messages) and enables PTC enforcement.        
Software cutout functionality can be employed during operational scenarios involving the loss of communication with a WIU which is monitoring a wayside device (e.g., a signal device, a switch/point, or a hazard detector), for example. Some specific example procedures implemented by the railroads are as follows:                Signal at STOP is covered within ITC-PTC using communication between the dispatcher and the train engineer, a special form of movement authority and communication between the office- and locomotive segments.        Switch is covered by procedure where the train engineer can manually enter the position of the switch on the human-machine interface (HMI) of the OBU after he/she verified that the switch is properly aligned.        Hazard Detectors can be integrated with a signal system or in a standalone configuration. The former case is covered by signal at STOP (if a hazard is detected). The latter is covered by procedures using communication between the dispatcher and the train engineer and allows movement at restricted speed.        